Cylindrical screen method for paper manufacturing

ABSTRACT

A CYLINDRICAL SCREEN-TYPE MACHINE FOR PAPER MANUFACTURE IS OPERATED SUCH THAT WHITE WATER WHICH FILTERS TO THE INTERIOR OF A CYCLINDRICAL SCREEN DOES NOT SPLASH ONTO A PAPER LAYER FORMED ON THE OUTER SURFACE OF THE CYLINDRICAL SCREEN WHEN THE WHITE WATER IS LATER THROWN OFF BY CENTRIFUGAL FORCE. THE EFFECTIVENESS IN OPERATION OF THE PRESENT MACHINE IN PREVENTING THE PAPER PRODUCED FROM BEING SOILED BY SPLASHING WHITE WATER INCREASES WITH INCREASING SPEED OF ROTATION OF THE SCREEN CYLINDER.

' March 19.74 KAZUMASA WATANABE CYLINDRICAL SCREEN METHOD FOR PAPER MANUFACTURING 2 Sheets-Sheet 1 Filed Dec. 27, 1971 Fig .I PRIOR ART March 5, 1974 KAZUMASA WATANABE 3,795,516

CYLINDRICAL SCREEN METHOD FOR PAPER MANUFACTURING 2 Sheets-Sheet 2 Filed Dec.

United States Patent Office Patented Mar. 5, 1974 CYLINDRICAL SCREEN METHOD FOR PAPER MANUFACTURING Kazumasa Watanabe, Fuji, Japan, assignor to Mitsuoki Iron Works Co., Ltd., Fuji, Japan Filed Dec. 27, 1971, Ser. No. 212,080

Claims priority, application Japan, June 21, 1971,

46/43:,915 Int. Cl. D21f 1/60, 11/06 US. Cl. 162-214 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to an improved method for operation of cylindrical screen-type paper manufacturing machines wherein paper stock is charged onto a cylindrical screen from sectional vats.

Cylindrical screen-type machines are known in the art such as that shown in FIG. 1. As can be seen from FIG. 1, paper stock from vat 2 is charged onto the cylindrical screen 1 at a point preceding, relative to the direction of rotation of the cylinder, the upper dead point 1 of the cylindrical screen 1. White water in the paper stock is filtered inward through the cylindrical screen under the head pressure of applied paper stock from vat 2 while the paper portion thereof is deposited on the cylindrical screen forming a paper layer thereon. The paper layer is, by couch roll 3, made to adhere to a conveying belt 4 made of a material such as felt. The paper layer is then transferred for subsequent processing such as to pressing or drying units in the manufacturing operation. Since the conveying belt 4 comes into contact with cylindrical screen 1 at point b beyond point a where the paper stock from the vat is charged onto the cylindrical screen, it applies a surface pressure on the upper outer surface of the paper stock on the cylindrical screen between the point b and point where couch roll 3 comes into cou tact with the outer surface of the conveying belt 4 on the cylindrical screen. Therefore, white water is filtered inward through the cylindrical screen not only between the points a and b under the head pressure during application of paper stock from the vat, but also the Water content of the paper layer is eliminated to the interior of the cylindrical screen between points b and c under the surface pressure mentioned above, and further at point 0 under pressure applied by the couch roll on the conveying belt 4 disposed on cylindrical screen 1 allowing a paper layer to be formed. The eliminated water which has been filtered onto the cylindrical screen is, under centrifugal force created by the rotation of the cylindrical screen, thrown off the exterior of the screen beyond the point where the couch roll comes into tangential contact with the cylindrical screen. Thus, there is a danger in prior art devices of this water splashing onto the paper layer which adheres to the conveying belt.

The above-mentioned tendency becomes more likely with increases in the revolving speed of the cylindrical screen and of the conveying speed of the belt during the speed-up of the paper manufacturing process. This tendency for splashing of white water is the main reason that the revolving speed of the cylindrical screen cannot be increased above a certain limit.

It has now been found that by practice of the present invention, there is provided and a method for effectively avoiding the splashing onto the paper layer of white water which is filtered onto the cylindrical screen which is subsequently thrown off under the centrifugal force created by rotation of the cylindrical screen, as the revolving speed of the cylindrical screen is increased.

The present invention will be described hereafter with reference to the embodiments shown in the accompanying drawing.

FIG. 1 is a schematic side view of a prior art paper making cylindrical machine of the conventional vat type; and

FIG. 2 through FIG. 8 show schematically side views of the embodiments of the machines provided by this invention.

In order to realize the above-mentioned aim, an endless screen 5 is applied on cylindrical screen 1 at least between point a and point 0. After having passed point 0, endless screen '5 may leave the outer surface of the cylindrical screen adjacent the depositing location of conveying belt 4 or at a location separately from it.

Consequently, according to the present invention, the paper stock from vat 2 is poured onto the endless screen 5 at point a of the cylindrical screen 1. White water is filtered through the endless screen and the cylindrical screen. Conveying belt 4 presses the paper stock onto the endless screen 5 and the cylindrical screen, forming a paper layer on endless screen 5. The paper layer is thus further dewatered between points b and 0 under surface pressure created by conveying belt 4 on the paper stock disposed on the endless screen 5, the latter being supported on the outer surface of the cylindrical screen. At point 0, the paper layer, squeezed between the conveying belt 4 and endless screen 5, is dewatered further by the external tangential pressure of the couch roll which contacts conveying belt 4 as it moves with the paper layer from the endless screen 5 and the cylindrical screen 1. Since endless screen 5 travels at the same speed as the linear velocity of the cylindrical screen, the splashes of white water are thrown off by the cylindrical screen after passing point c. And since the white water adheres to the cylindrical screen at the surface, due to centrifugal force, the White water comes into contact with, and is retained on, the endless screen due to the viscosity of the white water. Thus, the splashes of water fall far in the running direction by attaching to the endless screen thus making it possible to prevent white Water from otherwise being splashed on the paper layer by centrifugal force. For this purpose, it is necessary for endless screen 5 to come into contact with the cylindrical screen at a point ahead of point a, from, for example, the neighborhood of the lower dead point a of the cylindrical screen as shown in FIG. 2 and those figures following. However, when the endless screen 5 passes beyond the point 0, it should be separated from the cylindrical screen.

In the embodiment shown in FIG. 2, the endless screen 5, after passing beyond point c, leaves the cylindrical screen near the couch roll 3 alongside of the conveying belt 4. The endless screen is then curved and travels horizontally to the location of return roll 6 where it is again curved back and separated from the conveying belt 4. The endless screen 5 is returned to point a. where it comes into contact with the cylindrical screen. In order to wash the endless screen 5, a washing device 7 can be installed at a point located between the return roll 6 and point 0! where the endless screen 5 comes into contact with the cylindrical screen again. A drain tank 8 can be provided to receive the white water which is thrown off endless screen 5. A touch roll 9 can be installed externally and in contact with the couch roll 3 in order to further press out water from the paper layer by squeezing the paper layer between conveying belt 4 and endless screen 5. A suction device 10 can be provided against the return roll 6 in order to assure the adherence of the paper layer to the conveying belt 4 at the location where the endless screen departs the surface of the paper layer.

In the embodiment shown in FIG. 3, conveying belt 4 carries the paper layer around much roll 3 and on to the next paper making unit while endless screen continues to travel horizontally along straight line 5' after passing beyond the point c where it leaves the outer surface of the cylindrical screen. Thus, endless screen 5 may leave the cylindrical screen separately from conveying belt 4. The endless screen changes direction at return roll 11 and returns to lower dead point d of the cylindrical screen from where it enters another cycle.

However, as shown in FIG. 4, return roll 11 and second couch roll 12, which comes into external contact with the return roll 11, can be installed at a point beyond couch roll 3 in order to keep the conveying belt 4 and the endless screen 5 together along straight line 5', while separating them thereafter at second couch roll 12. Moreover, second couch roll 12 can be placed separately from the return roll 11 as illustrated in phantom in FIG. 4.

If necessary, plate 13 can be provided under the straight course 5' of the endless screen 5 in order to cut the flow of water being discharged from between cylindrical screen 1 and endless screen 5 at the departing location thereof, and a suction device 14 can be installed in order to effect dewatering of the endless screen 5.

The embodiment shown in FIG. 5 is a modification of that shown in FIG. 2. Conveying belt 4 together with endless screen 5 leaves the surface of the cylindrical screen at the location of couch roll 3. After travelling vertically upward, the endless screen is returned to the return roll 11 while the conveying belt 4 changes direction at the contact point between return roll 11 and the extremely touching second couch roll 15.

The embodiment shown in FIG. 6 is a modification of that shown in FIG. 4. Conveying belt 4 and endless screen 5 leave the circumferential surface to the cylindrical screen together and travel horizontally to the location of turn roll 16 where they change direction and rise upward vertically. Then, similarly to the embodiment of FIG. 5, the endless screen is turned back at return roll 11 and returned, while the conveying belt is curved at the second couch roll 15 while carrying the paper layer into the next paper manufacturing unit. If necessary, touch roll 9 can be installed in external contact with turn roll 16 in order to press water out of the paper layer squeezed between the conveying belt 4 and the endless screen 5.

Moreover, such as in the embodiments shown in FIG. 5 and FIG. 6, the paper layer can be dewatered by a suction device 19 such as one formed by a suction box placed within the interval 18 where the conveying belt and the endless screen squeeze the paper layer in between and travel upward.

In a similar fashion to the embodiments shown in FIGS. 4 and 6, the return roll 11 can be a wire-made cylinder type roll, having a surface permeable to air and working in cooperation with second couch rolls 12 and 15 in dewatering the paper layer. Thus, the water content can flow into the rolls interior and fall into the drain tank, from which water is discharged at an end of the roll.

FIG. 7 is the flow sheet for a series of stages using the embodiment shown in FIG. 5, through which runs the same lower surface of conveying belt 4. FIG. 8 is the flow sheet for a series of the machines shown in FIG. 6 through which runs the same lower surface of the conveying belt, using as the last stage paper making machine, the embodiment shown in FIG. 2.

In summary, according to the present invention, it is clear that the paper layer is formed on endless screen 5 running on the cylindrical screen in the embodiments shown respectively in FIG. 2 through 6 and in every embodiment shown in FIG. 7 and FIG. 8. This endless screen leaves the outer surface of the cylindrical screen after passing beyond point c where the couch roll and the cylindrical screen' come into contact externally, the water content is filtered into the interior of the cylindrical screen While the white water thrown olf of this cylindrical screen, by centrifugal force of the revolving cylindrical screen, is made to adhere by nature of the viscosity of the water, to the surface of the endless screen as it comes into contact with the cylindrical screen. For this reason, the splashing effect on the rejected white Water in prior art devices by the rotation of the cylindrical screen has been eliminated, thereby avoiding possible damage to the paper layer.

And since the endless screen travels at the same speed as the linear velocity of the cylindrical screen, when the rotation speed of the cylindrical screen is increased, in order to speed-up the process, the running speed of the endless screen is also accelerated. For this reason, the white water thrown off the cylindrical screen by centrifugal force of the cylindrical screen is more effectively guided to the endless screen as the speed increases. The influence of the centrifugal force to splash white water onto the paper layer is thus eliminated, this being a van! favorable result.

After the paper stock is filtered by letting the white Water flow to the cylindrical screen and through the end less screen, i.e., at point a, the paper layer is formed by dewatering under surface pressure created by the conveying belt while being squeezed between the conveying belt and the endless screen, and under the linear outer contact pressure created by the couch roll on the conveying belt. Therefore, the texture of the paper layer is not at all impaired by the dewatering process and thanks to the special feature of the endless screen, the water content of the paper layer can be sufficiently eliminated making it possible to manufacture paper with very high efiiciency.

What is claimed is:

1. In a method for paper manufacture wherein paper stock is dewatered on the outer surface of a rotating cylindrical screen to form a paper layer which is subsequently made to adhere to a conveying belt by a couch roll installed at a point some distance beyond the upper dead point of the cylindrical screen, the improvement which comprises the steps of:

(a) passing an endless screen over the outer surface of the rotating cylindrical screen in an interval between a point ahead of the site where the paper stock is initially dewatered on the outer surface of the cylindrical screen and a point at which the couch roll comes into contact with the cylindrical screen, said endless screen having the same speed as the linear velocity of the cylindrical screen;

(b) pouring paper stock onto the endless screen at the site where the paper is initially dewatered on the outer surface of the cylindrical screen;

(0) forming the paper layer in said interval by allowing the white water from the paper stock to filter through the endless screen and the outer surface of the cylindrical screen;

(d) contacting the paper layer formed on said endless screen with the conveying belt immediately before said upper dead point;

(e) adhering the paper layer to the conveying belt at the couch roll location;

(f) separating the endless screen from the outer surface of the cylindrical screen at the couch roll location and returning the endless screen to the point ahead of the site where the paper stock is poured;

(g) throwing off white water from the cylindrical screen and on to the separated portion of the endless screen; and

5 6 (h) recovering white water from the separated portion 3,236,724 2/1966 Wahlstrtim 162-318 X of the endless screen in a drain tank, whereby said 3,565,757 2/ 1971 Jordansson 162318 X white water is prevented by the endless screen from splashing on the paper layer adhering to the convey- LEON BASHORE, 'y EXamlIlel' ing belt. 5

References Cit d R. V. FISHER, Asslstant Exammer UNITED STATES PATENTS US. Cl.

1,514,556 11/1924 Milkey 162--319 X 1 335 1,534,620 4/1925 Wagner et a1 162319 

